In order to further increase the amount of information in broadcast waves transmitted via a broadcast satellite, there is, for example, a method of multiplexing left-handed and right-handed polarized waves, or vertically and horizontally polarized waves.
In order to receive polarized waves transmitted by this method, hitherto, a separation apparatus for separating multiplexed broadcast waves into left-handed polarized waves and right-handed polarized waves must be added to a conventional receiving apparatus (apparatus for receiving radio waves which are not multiplexed).
In particular, in a community receiving system (consisting of a community receiving apparatus and a terminal for each viewer) in a multi-family housing area or the like, the number of terminal units to which the received broadcast waves are distributed is great and many separation apparatuses must be added in order to receive the above-mentioned multiplexed broadcast waves.
Accordingly, various schemes are employed so as to receive multiplexed broadcast waves by adding a minimum number of separation apparatus to a conventional community receiving system.
FIG. 8 is a block diagram illustrating an example of the arrangement of a community receiving system. In FIG. 8, a parabolic antenna 11 is designed to receive radio waves in the RF (Radio Frequency) band, which are multiplexed by right-handed polarized waves and left-handed polarized waves (or vertically polarized waves and horizontally polarized waves) transmitted from a broadcast satellite (not shown). A low noise block (LNB) converter 12 is designed to separate the radio waves in the RF band received by the parabolic antenna 11 into left-handed polarized waves and right-handed polarized waves, convert the waves to signals in the IF (Intermediate Frequency) band (hereinafter referred to "IF signals"), and feed them to distributors 13a and 13b.
The distributors 13a and 13b distribute the IF signals of the left-handed polarized waves and the IF signals of the right-handed polarized waves to multi-switches 14a and 14b, respectively. The multi-switches 14a and 14b select either the IF signals of the left-handed polarized waves or the IF signals of the right-handed polarized waves in accordance with an individual polarized wave switching signal fed from each terminal unit (consisting of a receiver 15a through 15d and a television receiver 16a through 16d) of each subscriber and supplies the IF signals to each terminal unit.
The receivers 15a to 15d output a polarized wave switching signal to multi-switches 14a and 14b on the basis of the operation by the viewer, input the IF signals of the left-handed polarized waves or the IF signals of the right-handed polarized waves which are selected in accordance with the polarized wave switching signal and performs a process for converting the signals to the RF signals of a still lower frequency, and finally feed the signals to the television receivers 16a to 16d. The television receivers 16a to 16d extract video and sound signals from the signals fed from the receivers 15a to 15d and output these signals to make a display.
The operation of the above-described prior art will be described in greater detail below.
The multiplexed broadcast waves transmitted from a broadcast satellite (not shown) are received by the parabolic antenna 11. The LNB converter 12 separates the received broadcast waves into radio waves of left-handed and right-handed polarized waves and converts them into IF signals, and finally feeds the IF signals to the distributors 13a and 13b, respectively. The distributors 13a and 13b distribute the IF signals of the left-handed polarized waves and the IF signals of the right-handed polarized waves to the multi-switches 14a and 14b, respectively.
The multi-switches 14a and 14b select either one type of the IF signals of the left-handed polarized waves or the IF signals of the right-handed polarized waves in accordance with a polarized wave switching signal fed from the receivers 15a to 15d and feed the IF signals to the receivers 15a to 15d.
With the above-described arrangement, each viewer specifies either one type of the left-handed polarized waves or the right-handed polarized waves by a predetermined operation. Thereupon, the multi-switches 14a or 14b automatically selects either one type of these signals, making it possible to view a desired broadcast (program).
FIG. 9 is a block diagram illustrating another example of an arrangement of a community receiving system. Those components in FIG. 9 which are the same as those in FIG. 8 are given the same reference numerals and, therefore, a description thereof is omitted.
Receivers 21a to 21d receive the IF signals of the left-handed and right-handed polarized waves fed from the distributors 13a and 13b through separate signal cables and select these signals by a built-in switch (not shown). Then, a process for converting the selected IF signals into RF signals of a still lower frequency is performed, after which the RF signals are output to the television receivers 16a to 16d.
Other points of this arrangement are the same as those in FIG. 8.
The operation of the example shown in FIG. 9 will be described in greater detail below.
The parabolic antenna 11 receives radio waves in the RF band transmitted from a broadcast satellite (not shown). The LNB converter 12 separates the received radio waves into the radio waves of the left-handed and right-handed polarized waves and converts the radio waves into the IF signals, and then feeds the IF signals to distributors 13a and 13b, respectively.
The distributors 13a and 13b distribute and feed the input IF signals corresponding to the left-handed and right-handed polarized waves to each of the receivers 21a to 21d through separate cables. The receivers 21a to 21d select either one type of the IF signals corresponding to the left-handed or right-handed polarized waves fed from distributors 13a or 13b, perform a process for converting the IF signals into RF signals of a still lower frequency, and then output the RF signals to the television receivers 16a to 16d.
With the above-described arrangement, each viewer may operate the receivers 21a to 21d in order to select and view desired programs contained in either the left-handed polarized waves or the right-handed polarized waves.
In the example shown in FIG. 8, two cables are required to transmit the IF signals of the right-handed and left-handed polarized waves from outdoors to indoors. There are problems in that since the number of distributions of the multi-switches 14a and 14b is limited to some extent, the multi-switches cannot be used in large-scale community receiving facilities. Further, multi-switches 14a and 14b are normally expensive, causing the cost of facilities to increase.
In the example shown in FIG. 9, there are problems in that since two cables for supplying the IF signals from the distributors 13a and 13b to each receiver are required for each terminal unit, a large quantity of cable must be newly laid, resulting in increased costs.